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Sarkar, C.K.G., Srivastava, P.S.L., Deshmukh, P.S. 2001. Grain growth rate and heat susceptibility index: Traits for breeding genotypes tolerant to terminal high temperature stress in bread wheat ( Triticum aestivum L.). Indian J. Genet. 61 :209

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Adenosine diphosphate glucose pyrophosphorylase (AGPase) is the rate limiting enzyme of starch biosynthesis that directly affects the wheat productivity. AGPase and grain growth rate (GGR) discerned to be following strict temperature regimen in wheat disomic chromosome substitution (DCS) lines. The first half of grain filling period had chromosome 1B and 2D as prominent players, whereas second half was mainly controlled by chromosomes 6A and 5B. Chromosome 2D had major contribution towards yield in a specific temperature range of 23 ± 1.5 °C during initial stages of grain filling which can serve as an effective early screening tool for terminal heat tolerance in wheat. Chromosome 2D with highest amylose content can also be utilized to produce low digestibility flour. Grain yield was found to be significantly associated with spikes/plant, grains/spike, grain weight/spike and plant biomass. Further, path analysis indicated that though grains/spike had less direct effect on grain yield but its indirect impact on grain yield via AGPase-21 activity was high.

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Terminal heat referred to as increase in temperature during grain filling, is one of the important stress factors for wheat production and is responsible for decline in wheat production in many environments worldwide. In order to meet the challenges of high temperature ahead of global warming, concerted efforts are needed to evaluate wheat genotypes for heat tolerance and develop genotypes suitable for such stressed environments. Twenty-seven advanced wheat genotypes developed for stress and normal environments by different research centres were evaluated during 2009–10 and 2010–11 under timely sown (normal) and late sown (heat stress) environments. Analysis of variance revealed that the genotypes differed significantly in grain filling duration (GFD), grain growth rate (GGR) and thousand-grain weight (TGW). Out of 27 genotypes, 16 were found to be tolerant for thousand-grain weight under late planting (heat stress) during 2009-10 but only 12 were tolerant during 2010–11. Many of the genotypes registered more reduction in thousand-grain weight during 2010–11 as compared to 2009–10; the temperatures during 2009–10 were higher. The differences in grain filling duration under two conditions during both seasons as well as difference in temperatures during first half of grain filling explain the reduction pattern in the genotypes. GFD had significant negative correlation with temperatures during post heading period and the difference in GFD under two environments had positive correlation with these temperatures. The reduction in GFD had regression of 33.3% on reduction in GGR and reduction in GGR had regression of 41.6% on reduction in TGW genotypes AKW 1071, DBW 17, HS 277, K 7903, K 9107, NW 1014 and RAJ 3765 had less sensitivity to stress environments during both years.

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A stock of disomic chromosome substitution (DCS) lines having specific chromosome of wheat variety C591 substituted in the background of rest of Chinese spring chromosomes, were used to analyze grain yield components as a function of enzyme activity of ADP–glucose pyrophosphorylase (AGPase), a starch biosynthesis enzyme in wheat grains. Associations between yield characteristics, grain growth rate (GGR) and AGPase enzyme activity of DCS lines suggested a major involvement of chromosome 3A, 4B, 7D and 2D in a temperature dependent manner. Assessment of AGPase assay at different developmental stages such as 14, 21, 28 days post anthesis (DPA) embodied that gene(s) for this enzyme are present on specific chromosomes and operate at different stages of grain development. The DCS line with 7D chromosome has a major contribution in determining the grain starch content. In this line, AGPase enzyme activity was highest at 21 DPA and was the most crucial determinant in its high GGR. Line 4B performed well at only early stage (14 DPA) suggesting that line 4B AGPase requires a lower temperature range for activation as compared to 7D line. Line 3A had substantially reduced (40%) test weights revealing the presence of few down-regulatory elements on chromosome 3A to reduce the activity of AGPase. The DCS line 2D showed higher test weights and grain number than all other lines ascribed to a consistent AGPase activity along with an efficient mechanism for translocation of photosynthates from source to sink. The chromosome 2D shows positive relation with yield attributes therefore, it can be employed to improve wheat productivity via analytical breeding programme.

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Sarkar, C.K.G., Srivastava, P.S.L., Deshmukh, P.S. 2001. Grain growth rate and heat susceptibility index: Traits for breeding genotypes tolerant to terminal high temperature stress in bread wheat ( Triticum aestivum L.). Indian J. Genetics and Plant

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. Sheikh , S. , Sikka , V.K. , Behl , R.K. , Kumar , A. 2010 . Grain growth rate and grain yield in relation to ADPglucose pyrophosphorylase activity in wheat ( Triticum aestivum L. em. Thell) under normaland late sown conditions

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Journal of Thermal Analysis and Calorimetry
Authors: Cornelia Marinescu, Ancuta Sofronia, Cristina Rusti, Roxana Piticescu, Viorel Badilita, Eugeniu Vasile, Radu Baies and Speranta Tanasescu

energy are reached. Xisheng Ye et al. [ 29 ] pointed out that the grain growth rate is small in the range below 780 °C. For the heating rate of 5 °C/min, in the temperature range of rutile transition, 800–1000 °C, it is likely that the structural phase

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